1. Field of the Invention
The present invention relates to a process for production of amorphous semiconductor material. More particularly, the invention relates to a process for producing amorphous semiconductor material by glow discharge decomposition.
2. Description of the Prior Art
Amorphous semiconductor films, particularly, amorphous silicon films, have heretofore been prepared by the so-called RF glow discharge decomposition process wherein a mono-silane (SiH.sub.4) gas, for example, is decomposed by application of an electrical discharge using high frequency electrical fields. The decomposed gas is deposited on a substrate to form a thin film. Also, amorphous semiconductor members have been prepared using a so-called DC glow discharge decomposition process whererin a thin film is formed in the same manner as in the RF glow discharge decomposition process except that a DC electric field is employed for the production of the discharge.
The amorphous silicon formed by these glow discharge decomposition processes is known to be markedly low in the mean density of states of a local level in an energy gap, specifically, 10.sup.17 to 10.sup.18 cm.sup.-3, which is different from that of other known processes such as the vapor-deposition process and a process based on sputtering in a hydrogen-free gas atmosphere. This is thought to be due to the fact that the Si-Si bond is cut or the defects resulting from an irregularity of atomic arrangement are compensated by 5 to 30 atomic percent of hydrogen contained in the film. As a result, the amorphous silicon formed by the glow discharge decomposition process can be controlled with respect to valency electrons to form either a p- or n-type semiconductor. This permits the production with amorphous silicon at low cost a large surface area light sensor or devices such as a solar battery, a large surface area photoreceptor, specifically, an electrophotographic light-sensitive member, or other such devices. Recently, the application of amorphous silicon for such devices has increasingly been studied.
In the previously-known glow discharge decomposition processes, however, the production rate is markedly low compared with other common vapor-deposition processes. For example, the Journal of Applied Physics, Vol. 48, No. 12, page 5227 (1977), reports that the production rate is about 0.1 to 0.5 .mu.m/min at most. If the film is deposited at a greater rate than the upper limit, the photoconductivity and film-forming properties of the layer obtained will be greatly degraded. For example, if the DC glow discharge decomposition process is carried out at a greater deposition rate than the above value, the uniformity of the film obtained will be greatly inferior, and at a film thickness of bout 10 .mu.m, no film-forming properties will be exhibited. Furthermore, experiments conducted by the inventors have revealed that the photoconductivity is lowered as the uniformity of the film deteriorates.
In the production of silicon amorphous semiconductor material by glow discharge decomposition, an improvement in the deposition rate of the amorphous semiconductor leads to a reduction in the production costs of the amorphous semiconductor.